The present invention relates to photothermographic materials exhibiting superior productivity and handleability during the manufacturing process and also exhibiting superior transportability and stackability when being subjected to thermal processing. The invention also relates to photothermographic materials having enhanced abrasion resistance and exhibiting superior image quality.
In the field of graphic arts and medical treatment, there have been concerns processing of photographic fims with respect to effluents produced from wet-processing of image forming materials, and recently, reduction of the processing effluent is strongly demanded in terms of environmental protection and space saving. As a photothermographic material for photographic use and capable of forming distinct black images exhibiting high sharpness, enabling efficient exposure by means of a laser imager or laser image setter known is a thermally developable silver halide photographic material.
Such a photothermographic material comprises a reducible silver source (e.g., organic silver salt), a catalytically active amount of photocatalyst (e.g., silver halide) and a reducing agent, which are dispersed in an organic binder matrix. The photothermographic material is stable at ordinary temperature and after exposure, forms silver upon heating, at a relatively high temperature through an oxidation-reduction reaction between the reducible silver source (which functions as an oxidizing agent) and the reducing agent.
In the photothermographic material used are organic silver salts such as a silver salt of a long chain fatty acid, as a reducible silver source. The organic silver salts can be obtained by mixing an aqueous soluble silver salt with an organic acid such as a long chain fatty acid. For example, after adding an alkali metal salt (e.g., sodium hydroxide, potassium hydroxide) to the organic acid to form an alkali metal soap of the organic acid (e.g., sodium behenate, sodium arachidate), the soap and an aqueous soluble silver salt such as silver nitrate are added by double jet addition to form an organic silver salt.
In such a process, however, it is difficult to alter all of the organic acid to an organic silver salt so that more than a small amount of the organic acid as a raw material remains as an impurity. Further, an organic acid was added to prevent photo-discoloration, as described in JP-A No. 50-59619 (hereinafter, the term, JP-A refers to an unexamined, published Japanese Patent Application).
Photothermographic materials are manufactured employing various coating techniques, including air doctor coating, blade coating, squeezing coating, reverse roll coating, gravure coating, spray coating and bar coating. In cases where two or more layers are coated employing these coating techniques, after the first layer has been dried, the second layer is formed, resulting in insufficient adhesion between layers and thereby leading to lowered production efficiency. An attempt to overcome such problems by simultaneous multi-layer coating, as described in JP-A 11-119375.
However, it was proved that when an image forming layer and a surface protective layer are simultaneously coated, there occurred problems such that an organic acid contained in the image forming layer diffused to the protective layer, forming precipitates on the surface, even when not incorporated into the protective layer. It was further proved that the thus precipitated organic acid deteriorated the physical properties of the surface, producing troubles in transporting or stacking when being subjected to thermal processing stage. Further, it was also proved that when photothermographic materials were processed at a temperature of 100xc2x0 C. or more using an automatic thermal processor, any contamination with the organic acid softened the surface protective layer, lowering resistance to abrasion.
Accordingly, it is an object of the present invention to provide a photothermographic material exhibiting superior productivity and handlability in the manufacturing process and also exhibiting superior transportability and stackability in thermal processing.
It is also an object to provide a photothermographic material exhibiting superior image quality without producing abrasion marks.
The object of the invention can be accomplished by the following means:
1. A photothermographic material comprising a support having one side of the support at least an image forming layer containing organic silver salt grains, light sensitive silver halide grains and a reducing agent and a surface protective layer, wherein when the photothermographic material is subjected to X-ray photoelectron spectroscopy with respect to surface element composition, the thereby obtained ratio of the number of carbon elements to the number of oxygen elements of the image forming layer side is not more than 9.
2. A photothermographic material comprising a support having on one side of the support at least an image forming layer containing organic silver salt grains, light sensitive silver halide grains and a reducing agent and a surface protective layer, wherein a layer farthest from the support contains a binder and an organic acid of not more than 5% by weight, based on the binder.